The invention of this application relates to a high toughness steel and to a method for manufacturing the same. More particularly, the invention of this application relates to a high toughness steel having an excellent toughness useful for a steel material used as steel for structural purposes such as steel bars, section steel, thin plates and thick plates and also relates to a method for manufacturing the same.
In a steel material which has been utilized as the steel for structural purposes, there is a problem that a prior-austenite grain boundary which is the weakest part or the inherent austenite grain boundary prior to conducting a mechanical process and a thermal treatment is broken whereby intergranular cracking is resulted and that a brittle fracture takes place.
For example, in the case of a tempered martensite steel, filmy carbides precipitate continuously in an a prior-austenite grain boundary and they restrict the plastic deformation near the grain boundary resulting in such a fracture in the grain boundary.
An object of the invention of this application is to suppress the fracture at a grain boundary caused by prior-austenite grain boundary and to offer a high toughness steel having an excellent toughness and a method for manufacturing the same.
This and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed specification and drawing, in which: